This invention relates to an improvement in attaching friction material to a clutch disc.
Clutch discs are used in clutch assemblies to transmit drive forces from a prime mover to an output shaft. Prior art clutch discs often have a plurality of backing plates each of which has friction material disposed on an outwardly facing surface. The backing plates are spaced circumferentially about the clutch disc, and are selectively engaged with a drive disc to transmit a rotational force drive to an output shaft. In the prior art, the friction material is typically attached to the backing plate, and the backing plate is riveted to the clutch disc.
One problem with the prior art backing plates is that, due primarily to unequal heat distribution, they often pull away from the clutch disc at a central location. Further, the center of the friction material tends to bear the greatest friction and forces. Thus, the friction material at the center of the backing plate heats to a higher temperature then other portions of the friction material. The coefficient of friction at the center of the friction material is then different than at the remainder of the friction material. This may cause the clutch facings to grab upon engagement producing "jerky" vehicular operation, particularly in heavy trucks. These problems are particularly acute with ceramic friction materials which may experience warpage or bowing distortion.
The prior art teaches spacing friction material portions to create air channels therebetween which cool select areas of the friction material. The prior art clutch discs have thus included large spaces between friction material portions. It would be desirable to increase the area covered by the friction material. These prior art structures have also not overcome the aforementioned bowing problem. Thus, it is desirable to improve the prior art backing plates.